1. Field of the Invention
The present invention relates to a light emitting device that can be applied to lighting for mobile phone backlight, display capable of displaying various types of data, light source for various types of sensors such as line sensor, indicator, and so on.
2. Description of the Related Art
Light emitting elements such as light emitting diode (hereinafter, occasionally referred to as an “LED”) and semiconductor laser (hereinafter, occasionally referred to as an “LD”) have been used as various types of light sources. Particularly, light emitting diodes capable of emitting light at high luminance higher than 1000 mcd have been developed, and are increasingly applied to lighting for mobile phone LCD backlight, character display board used outdoors or indoors such as large-scale full-color display. In the case to display complex characters such as JIS 2nd level Kanji, a very high resolution display is required.
On the other hand, the aforementioned light emitting elements generate heat when emitting light. Accordingly, in the case of high resolution display, if light emitting devices with the aforementioned light emitting elements mounted thereto are simply installed on a circuit board at high density, the heat generated by the light emitting elements causes property deterioration of members in the light emitting device or a malfunction.
As a light emitting device that has excellent heat dissipation properties and is suitable for high density installation, a light emitting device that has an insulating board with a hole for heat sink, a sub-insulating sheet laminated on the board for enclosing the hole, and a light emitting element mounted on the sub-insulating sheet above the hole is disclosed (Japanese Patent Publication No. 3469890). In addition, as a technique for improving heat dissipation properties, the publication discloses that another hole smaller than the light emitting element is formed on the sub-insulating sheet below the light emitting element so that the light emitting element is in direct contact with air, and that a conductive member is applied on or filled in the hole.
However, since the light emitting device proposed in the aforementioned patent publication has the structure where the light emitting device itself dissipates heat generated by the light emitting element, its heat dissipation performance is limited. Thus, further improvement is required.
Therefore, it is an object of the present invention is to provide a light emitting device that has excellent reliability and light-outgoing efficiency.